1. Field of the Invention
The present invention relates to a rotational angle detecting device for detecting the angle of rotation in various machines and equipments, for example, for detecting the angle of rotation for the purpose of controlling the rotation of a compact motor and also to a detector incorporated bearing assembly having its rotation detecting device incorporated therein.
2. Description of the Prior Art
A rotational angle detecting device capable of being incorporated in a small size machine or equipment and also capable of detecting the angle of rotation with high accuracy has been suggested, in which a magnetic sensor array is employed. (See, for example, the Japanese Laid-open Patent Publication No. 2004-37133 published Feb. 5, 2004.) In this known rotational angle detecting device, as shown in FIG. 22, the magnetic sensor array 45 including a plurality of magnetic sensor elements (MAGFETs) arranged therein is integrated on a sensor chip 42 together with a circuit 46 including a signal amplifying circuit, an AD converting circuit and a digital signal processing circuit, which sensor chip 42 is in turn arranged in face-to-face relation with a magnet 44 arranged on a rotating member 41. In this case, the magnet 44 is rendered to have an anisotropy in a circumferential direction about the axis of rotation O, and on the sensor chip 42, the magnetic sensor array 45 is arranged along each of the four sides of the imaginary rectangular shape.
With the rotational angle detecting device 43 so constructed as hereinabove described, an output of the magnetic sensor arrays 45 each extending along one of the four sides is read out by the signal amplifying circuit and the AD converting circuit to detect a distribution of magnetic fields developed by the magnet 44 and the angle of rotation of the magnet 44 is subsequently calculated by the digital signal processing circuit based on a result of such detection.
Although the detecting method is different from that used in the rotational angle detecting device 43 of a kind disclosed in the above mentioned Patent Document, a rotation detecting device has also been suggested, in which a plurality of magnetic sensor elements such as Hall elements are employed and the position and the movement of a magnet fixed to a rotatable body are detected by calculating respective output signals of the magnetic sensor elements.
In those rotational angle detecting devices, both of a substantial length of time to read out the respective outputs from the individual magnetic sensor elements and a calculation processing time to determine information on, for example, the angle of rotation from the read-out signals are required and, therefore, a time lag often occurs in a detection signal. For this reason, when the rotational speed of the rotating member is high, a deviation occurs between the actual rotational speed and the rotational angle detected and, therefore, there has been a problem that difficulty is encountered in using in the field of use where precise information on the position of rotation is required in real time. In other words, the operation of the rotational angle detecting device of the construction described above repeats a cycle of measurement of the magnetic field→angle calculation→angle output and, accordingly, angle data are outputted at intervals of a predetermined time corresponding to the cycle. Because of this, a problem has been recognized that the angle data outputted has a time lag corresponding to the length of time required to perform the angle calculation and no accurate information on the angle at the time of observation can be obtained. Also, where the rotation of the motor is to be performed by detecting the angle of rotation and the rotational speed with the use of this rotational angle detecting device, difficulty has been encountered in accurately detecting the angle of rotation and the rotational speed at an arbitrarily chosen time.